Ukraine has said it is doing all it can to secure the extradition from Libya of 19 of its citizens accused of being pro-Gaddafi mercenaries.

The group, which also includes three Belarusians and two Russians, was formally charged on Monday, eight months after they were detained.

The 24 accused insist they were working as oil industry contractors.

One of the Russians has told the BBC that their release could already have been secured through diplomacy.

In a phone interview, Aleksandr Shadrov, 59, told the BBC Russian Service that they had all been in Libya purely to service oil rigging equipment and that a good lawyer would "easily refute the case".

They deny the charges of preparing land-to-air missile launchers to shoot down planes taking part in the Nato-led mission to protect Libyan civilians.

The Russian embassy in Libya has told the BBC that it is doing all it can to secure the release of its citizens. Belarus says its three citizens had signed contracts to operate civil facilities in Libya and it is co-ordinating its efforts with the Russian and Ukrainian embassies.

The Ukrainian authorities said negotiations between Kiev and the Libyan authorities were already under way. A spokesman for the Ukrainian foreign ministry said a possible extradition of its 19 citizens was on the table, even though the two countries had no formal treaty.

Mr Shadrov believed the problem was that Russian officials had probably waited for "some sort of overarching authority [in Libya]. What they needed to do was reach an agreement with the commanding officer of the group holding us under guard."

The group who were detained as rebel fighters pursued the remnants of pro-Gaddafi forces last September are now being held near Tripoli at a Libyan Home Guard base.